Collaborative Research: The Role of Phytoplankton Ballast Material in Deterring Copepod Grazing

许多海洋原生动物(藻类和原生动物)被“装甲”，细胞壁加厚，鳞片覆盖，坚硬的“壳”(试验，经虫)，或格子状的“骨架”。据推测，这些矿床的演化功能是阻止放牧。然而，到目前为止，还没有直接测量原生动物的放牧率作为其矿物质含量的函数。二氧化硅特殊染色的最新发展和最先进的流式细胞仪技术使这些测量成为可能。这项研究直接测试了细胞矿物质配额与桡足类摄食率之间的关系。利用良好控制的藻类养殖技术，将创造出矿物盔甲相对程度不同的浮游植物细胞。矿物质载量将通过化学(化学消化)、肉眼(扫描电子显微镜)和光度(矿物质和细胞表面特定染料和流式细胞术)来确定。生物矿物提供的放牧保护将通过对选择过程背后的行为机制的详细检查(显微摄影)来检验，以对抗桡足类的捕食。初步的放牧实验表明，桡足类对生物矿物含量较低的细胞有强烈的偏好。这表明，戒备森严的细胞不太可能被包装成粪便颗粒，从而使浮游生物的矿物质含量与出口到深海的浮游生物分离。这意味着全球生物地球化学循环在一定程度上是由捕食者-猎物相互作用的生态和进化制约构成的。这项研究包括对摄取的颗粒和桡足类粪便颗粒的矿物质含量的测量。假设粪便颗粒中的矿物质含量越高，颗粒的密度就越大，从而导致更高的沉降速度。生物泵在隔离大气二氧化碳方面的作用在一定程度上是由粪便颗粒的快速下沉速度驱动的。这项提案中概述的实验将把桡足类食物的矿物质含量与粪便颗粒的矿物质含量联系起来。随后，直接视频观测将能够测量粪便颗粒的下沉率作为其矿物负荷的函数。智力优势：测量和了解控制有机物质流向沉积物的因素一直是许多大型海洋学项目(例如JGOFS和Antares)的重点。已提出用表层产量或矿物压载含量的指标来预测深海通量。然而，由于缺乏对驱动物质到达沉积物的质量和数量的潜在过程的机械理解，只有在机制保持不变的情况下，这些代理才是可靠的。需要关于桡足类和初级生产者之间直接相互作用的信息，以预测浮游植物/桡足类联系的变化将如何体现在将有机物生物泵送到深海中。广泛影响：该提案通过在三年项目中纳入三名学生，为本科教育做出了贡献。该提案有许多自成一体的子项目，这些项目将为有动力的本科生提供获得实践研究经验的特殊机会。学生将学习针对不同浮游植物的复杂养殖技术，参与放牧实验，并学习光学和微电影摄影的基础知识。此外，这项提议的经济成本很低，两名学生将在采样和鉴定浮游生物以及进行放牧实验方面获得宝贵的实地经验。我们实验室的学生将被要求每周开会，讨论问题、最近的成功和与他们特定主题相关的文献。将鼓励学生参加专业协会的会议和活动。该项目的成果还将有助于毕格罗实验室教育和推广方案的发展，最著名的是植物园项目及其为中学和高等教育的学习者和教师提供的相关实用程序(http://www.bigelow.org/phytopia/).

Many groups of marine protists (algae and protozoa) are "armored" with thickened cell walls, coatings of scales, hard "cases" (tests, loricas), or latticework "skeletons". The inferred evolutionary function of these mineral deposits is to deter grazing. However, to date there are no direct measurements of grazing rates on protists as a function of their mineral content. The recent development of silica specific stains and state of the art flow cytometry techniques enable these measurements. This study directly tests the relationship between the cellular mineral quota and the ingestion rates of copepods. Phytoplankton cells that differ in the relative degree of mineral armor will be created using well controlled algal rearing techniques. Mineral load will be determined chemically (chemical digestion), visually (SEM), and photometrically (mineral and cell surface specific dyes and flow cytometry). The grazing protection conferred by biogenic minerals will be examined against copepod predation with detailed examination (microcinematography) of the behavioral mechanisms that underlie the selective process.Preliminary grazing experiments show that copepods have a strong preference for cells with low biogenic mineral content. This suggests that heavily fortified cells are less likely to be packaged into fecal pellets, thus uncoupling the mineral content of plankton from what is exported to the deep ocean. This implies that global biogeochemical cycles are structured, in part, by the ecological and evolutionary constraints of predator-prey interactions. This study includes measurement of the mineral content of the ingested particles and of the fecal pellets of copepods. The hypothesis is that a higher mineral content in the fecal pellet will increase the density of the pellet and therefore, lead to a higher settling velocity. The role of the biological pump in sequestering atmospheric CO2 is driven, in part, by the rapid sinking rates of fecal pellets. Experiments outlined in this proposal will link the mineral content of the copepod diet with the mineral content of the fecal pellet. Subsequently, direct video observations will enable measurement of the sinking rates of fecal pellets as a function of their mineral load.Intellectual Merit: Measuring and understanding the factors that control the flux of organic material to the sediments has been the focus of numerous large oceanographic programs (e.g. JGOFS and ANTARES). Proxies of surface production or mineral ballast content have been proposed to predict deep ocean fluxes. However without a mechanistic understanding of the underlying processes driving the quality and quantity of material reaching the sediments, these proxies are robust only when the mechanisms remain constant. Information on the direct interactions between copepods and primary producers is needed to predict how changes in the phytoplankton/copepod link will manifest in the biological pump of organic matter to the deep ocean.Broader Impacts: The proposal contributes to undergraduate education by incorporating three students during the three year project. The proposal has numerous self-contained sub-projects that will provide exceptional opportunities for motivated undergraduate students to receive hands on research experience. Students will learn sophisticated culturing techniques for different phytoplankton, participate in grazing experiments and learn the fundamentals of optics and microcinematography. In addition, at little financial cost to this proposal two students will gain valuable field experience in sampling and identifying plankton and conducting grazing experiment. Students in our lab will be required to meet weekly to discuss problems, recent success, and pertinent literature to their specific topic. Student participation at meetings and activities of professional societies will be encouraged. Results of the project will also contribute to the development of Bigelow Laboratory educational and outreach programs, most notably the Phytopia project and its allied utilities for learners and teachers at secondary and tertiary levels (http://www.bigelow.org/phytopia/).